GE 845 Instruction Manual page 221

CHAPTER 4: SETPOINTS
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
VOLTAGE INCREMENT PER TAP
Range: 0.01 to 20.00 kV in steps of 0.01 kV
Default: 0.50 kV
Enter the voltage increment per tap change.
BCD BIT 1- 5 INPUT
Range: Off, Contact Input 1(X), Virtual Input 1(X), Remote Input 1(X)
Default: Off
The six BCD inputs require selection of contact inputs, virtual inputs, or remote inputs.
The tap position is detected by the state combination of high/low bits received from the
tap changer mechanism.
BCD BIT 6 INPUT:
Range: Off, Contact Input 1(X), Virtual Input 1(X), Remote Input 1(X)
Default: Off
This input provides the configuration of the BCD Bit 6 input. The tap position provided by
the transformer can be either positive from 1 to 39, or positive and negative from -19 to
19.
BCD BIT 6 input provides the configuration of the positive BCD BIT 6 or the sign (-) of the
BCD code.
The selection of BCD BIT 6 working mode is made according to the TAP MIN setting.
When the TAP MIN setpoint is configured with a negative value, the BCD BIT 6 will
provide the sign(-) of the BCD.
Hence, the maximum range for BCD tap detection of negative and positive taps goes
from -19 to +19.
When, TAP MIN setting is positive the BCD BIT 6 INPUT provides the BCD 20 code. As a
result, the full BCD range goes from 1 to 39.
INVERSE TAP POSITIONS
Range: Disabled, Enabled
Default: Disabled
When "Disabled", increasing the tap position increases turns and hence the winding
voltage, used also for automatic compensation of the currents mismatch, which
otherwise could be seen as differential current upon changing tap. This usually is the
case when the OLTC(On-Load Tap Changer) is installed on the winding connected to the
load.
When "Enabled", increasing the tap position will decrease the ampere-turns of the
winding. When the OLTC is installed on the winding connected to the source, increasing
the tap will have to decrease the turns, to maintain constant voltage at the secondary
winding connected to load. This usually is the case when the OLTC is installed on the
winding connected to the source.
Binary Coded Decimal (BCD) inputs
To configure the BCD decoder inputs into an I/O card the BCD BIT x INPUT setpoints must
be programmed.
• With 4 BCD bits programmed, only 9 tap positions can be detected.
• Five BCD bits programmed can be used for detection of up to 19 tap positions.
• With all 6 BCD bits programmed, the relay can detect up to 39 tap positions.
The physical connection between the output BCD decoder and the I/O card (for five BCD
bits programmed) is shown in the next figure: An example of BCD decoder connections to
an IO_C card for up to 19 taps.
The selection of the suitable setting depends on the customer's criteria. In both cases,
when the BCD format is chosen, the neutral tap position must be entered.
SYSTEM
4–117